Terbinafine is known as an effective antifungal agent belonging to the allylamine family and is used for the treatment of tinea unguium. Tinea unguium is an intractable disease caused by the intrusion of Trichophyton into nails and is characterized by conditions such as cloudiness, thickening, and deformation of a nail surface.
At present, oral administration of antifungal agents such as terbinafine or itraconazole belonging to the triazole family on a long-term basis is the mainstream treatment of tinea unguium, but it has problems such as critical side effects, such as hepatopathy caused by taking antifungal agents for a long period of time, and an interaction with other agents. It is reported that, generally, the dose of the oral formulation of terbinafine is 125 mg/day (to be taken once a day after a meal) for an adult; the terbinafine concentration in plasma reaches a steady state in 10 weeks and is 280 ng/mL in average; and the terbinafine concentration in nails reaches a steady state in 12 weeks and is 0.78 ng/mg in average.
On the other hand, several external preparations for nails in which an antifungal agent is mixed have been proposed because it is expected that the external preparations for nails have low drug permeation into plasma and can reduce the side effects of the antifungal agent and that the high concentration of the drug in nails can be more easily achieved than an oral agent. However, since a sufficient permeation amount of the drug into nails having high barrier ability cannot be obtained, these external preparations not necessarily have a high therapeutic effect under the present circumstances.
Further, an adhesive patch containing an antifungal agent has also been proposed from the point that administration is convenient (Patent Literatures 1 to 4). In the case of these adhesive patches, the use feeling is improved compared with the external preparations which are not adhesive patches such as liquid formulations, and the drug permeability into nails is improved because direct application to nails allows the drug to sustainingly act on the nails; but a permeation amount of the drug sufficient for the treatment of tinea unguium is not yet achieved. Furthermore, an attempt to effectively permeate a drug into nails has been performed in recent years by mixing terbinafine at a high concentration in a pressure sensitive adhesive of an adhesive patch (Patent Literatures 5 to 7).